Brown burger and onions. Season burger to taste. Shred cabbage.
Spray a casserole dish and place one layer of shredded cabbage on bottom. Top with seasoned cooked ground beef and onions. Top with remaining cabbage. Pour undiluted can of tomato soup over all. Spread over and pierce with fork several times. Cover with foil.
Bake in preheated 350°F oven for 40 minutes. Remove foil and bake an additional 5 minutes. Remove from oven; allow to sit for 8 minutes. Serve.